Plants of the family Asclepiadaceae are known to be extremely poisonous. A well-known representative of the Asclepiadaceae is Calotropis procera. Extracts from Calotropis procera plants have traditionally been used as an abortifacient, for infanticide, for rheumatic pain and to produce a purgative. The plant is poisonous, but has been used in small amounts for folk remedies for various ailments, and the plant continues to be studied for anti-coagulant and anti-cancer properties. The stems, flowers and leaves of Calotropis procera plants are known to contain certain compounds known as cardenolides. Examples of cardenolide glycosides found in C. procera include asclepin, voruscharin, uscharin, uscharidin, calotropin, calactin, calotoxin, calotropagenin and uzarigenin. Recently, cytotoxic activity has been attributed to these cardenolide glycosides, and they are exploited in human therapies for treating cardiac insufficiencies.
It has been described that the cardenolide uscharin is particularly useful for medical purposes. Uscharin has been isolated and its chemical structure was determined (structure I).

Compositions comprising uscharin or salts thereof have been reported to be usable for treatment of medical conditions related to cell proliferation. For example, U.S. Pat. No. 6,342,490 and WO-9852562 both describe compositions comprising uscharin or salts thereof and the use of uscharin to combat cell proliferation, e.g. in the treatment of cancer.
Some of the known cardenolide glycosides, f.e. calotropin and uzarigenin, are cytotoxic for cell cultures but are not mentioned to show in vivo tumor-inhibiting activity. Also uscharin has been shown to have some cytotoxic activity on tumor cells in vitro. In addition, uscharin was also described to have in vivo tumor-inhibiting effects, as for instance described in U.S. Pat. No. 6,342,490. Derivatives of uscharin have not been reported so far to be useful for medical applications.
It is a general object of the present invention to provide novel cardenolide glycosides, which have a cytotoxic activity. It is another general object of the present invention to provide novel cardenolide glycosides, which can be exploited in medical applications.